Transformers are components widely used in the electronics industry, in particular in radio frequency electronic devices (for example, transceivers) and in power electronic devices (for example, voltage transformers).
The constant process of miniaturization (scaling) of the electronic circuits and a consequent development of (electronic) System-on-Chip (SoC) devices (i.e., complex electronic systems integrated on a chip semiconductor material (for example, silicon)), has led to the provision of miniaturized integrated inductors and, consequently, to the provision of integrated transformers that allow the manufacturing of a SoC comprising such (integrated) radio frequency circuit portions and/or (integrated) power circuit portions.
In general, an integrated transformer, simply “transformer” in the following, comprises two or more (integrated) inductors, each formed by means of a strip of metallic material (e.g., aluminum or copper) with a spiral arrangement. For example, the metallic material of the inductors is comprised in a metallization layer of an integrated circuit of which the inductor is part.
Due to the extremely small size of these inductors, operating voltages to which inductors are subjected during their operation can lead to a deterioration thereof (leading to a reduction of their operating efficiency), up to their complete destruction (which prevents the proper functioning of a SoC in which they are integrated).
For example, by considering a voltage transformer circuit, it usually comprises a primary winding that comprises an inductor formed by a corresponding metallization layer and a secondary winding that comprises another inductor formed by a corresponding different metallization layer. The two windings are separated by a layer (or layers) of insulating material. In a structure of this type, the operating voltage present between the two windings of the transformer or an extraordinary event (such as a peak in the supply voltage) on the power grid where the transformer is connected or a voltage stress applied during tests performed on the transformer (required for certification of galvanic isolation thereof) may require an electric field between the two windings that generates harmful effects on the transformer. In particular, in correspondence of an (or more) outer coil(s) of the inductor that forms the primary winding (i.e., the transformer winding to which is applied a potential difference having the greater value), subjected to a high intensity voltage (e.g., provided by an electric network or from a power supply block), the physical phenomenon called fringing effect may occur.
The fringing effect causes a local concentration of the electric field in correspondence of an edge (or fringe) of the outer coil of the inductor which forms the upper winding, henceforth referred to as the primary winding. This local concentration of the electric field due to the effect of the edge may cause a deterioration, up to a rupture (or burning), of the primary winding, thereby compromising, or even preventing, the operation of the transformer (and therefore of a SoC to which the circuit belongs).